Method and compositions for producing disulfide-linked trimeric TNF family of cytokines and their use

ABSTRACT

Compositions of TNF family of cytokines in covalently linked trimeric forms are disclosed. The resulting fusion proteins are secreted as disulfide bond-linked homotrimers, which are more stable in structure and therapeutically more efficacious than their native counterparts.

FIELD OF THE INVENTION

The present invention relates to methods for protein expression, and more specifically, for creating and expressing secreted, disulfide-linked and biologically active trimeric proteins from TNF family of cytokines.

BACKGROUND OF INVENTION

In multicellular organisms, such as mammals, cells communicate with each other by signal transduction pathways, in which a secreted ligand (e.g. cytokines, growth factors, or hormones) binds to its cell surface receptor(s), leading to receptor activation. The receptors are membrane proteins, which consist of an extracellular domain responsible for ligand binding, a central transmembrane region followed by a cytoplasmic domain responsible for sending the signal downstream. Signal transduction can take place in the following three ways: paracrine (communication between neighboring cells), autocrine (cell communication to itself) and endocrine (communication between distant cells through circulation), depending on the source of a secreted signal and the location of target cell expressing a receptor(s). One of the general mechanisms underlying receptor activation, which sets off a cascade of events beneath the cell membrane including the activation of gene expression, is that a polypeptide ligand such as a cytokine, is present in an oligomeric form, such as a homo-dimer or trimer, which when bound to its monomeric receptor at the cell outer surface, leads to the oligomerization of the receptor. Signal transduction pathways play a key role in normal cell development, differentiation and immune surveillance against cancer, as well as in response to external insults such as bacterial and viral infections. Abnormalities in such signal transduction pathways, in the form of either underactivation (e.g. lack of ligand) or overactivation (e.g. too much ligand), are the underlying causes for pathological conditions and diseases such as arthritis, cancer, AIDS, and diabetes.

One of the current strategies for treating these debilitating diseases involves the use of receptor decoys, such as soluble receptors consisting of only the extracellular ligand-binding domain, to intercept a ligand and thus overcome the overactivation of a receptor. A good example of this strategy is the creation of Enbrel®, a dimeric soluble TNF-α receptor-immunoglobulin (IgG) fusion protein by Immunex, which is now part of Amgen. Anti-TNF-α biologics have now become the standard of care for a host of autoimmune diseases. The TNF family of cytokines is one of the major pro-inflammatory signals produced by the body in response to infection and tissue injury. However, abnormal production of these cytokines, for example, in the absence of infection or tissue injury, has been shown to be one of the underlying causes for diseases such as arthritis and psoriasis. Naturally, a TNF-α receptor is present in monomeric form on the cell surface before binding to its ligand, TNF-α, which exists, in contrast, as a homotrimer. Accordingly, fusing a soluble TNF-α receptor with the Fc region of immunoglobulin G1, which is capable of spontaneous dimerization via disulfide bonds, allowed the secretion of a dimeric soluble TNF-α receptor. In comparison with the monomeric soluble receptor, the dimeric TNF-α receptor II-Fc fusion has a greatly increased affinity to the homo-trimeric ligand. This provides a molecular basis for its clinical use in treating rheumatoid arthritis (RA), an autoimmune disease in which constitutively elevated TNF-α, a major pro-inflammatory cytokine, plays an important causal role.

In contrast, abnormalities in the production of certain TNF family of cytokines seems to be linked to failure in immune surveillance against cancer. In fact the founding member, TNF-α was initially identified as a cancer cell killer and so named as TNF (tumor necrosis factor). Now, it is known that several members of TNF family of cytokines, including TNF-α, FasL and TRAIL/Apo2L, have the ability to potently elicit cancer cell killing via either apoptosis or necrosis. However, it turns out that overexpression of TNF-α and FasL are toxic to mammals as they elicit potent inflammatory responses. So far only TRAIL/Apo2L retains the characteristics for being cancer-specific killer via apoptosis and has been extensively studied as an anti-cancer biologics (Wang and El-Deiry, 2003). Recombinant TRAIL/Apo2L (Dulanermin/AMG 951) produced from E. coli by Amgen and Genentech showed promising results in preclinical xenograft animal models (Kelley et al., 2001) as well as in Phase I clinical trials against multiple cancers (Soria et al., 2010). However, it failed in several Phase II trials due to lack of efficacy albeit good safety profile (Soria et al., 2011). The lack of efficacy has been linked to Dulanermin's poor pharmacokinetic profile, with very short systemic half-life in mammals; this is likely due to its small molecular weight (˜60 kDa) and the instability of its non-covalently linked trimeric structure, both ultimately leading to its rapid elimination via renal filtration (Kelley et al., 2001). Thus, trimerization via covalent bond linkage may stabilize TRAIL/Apo2L trimeric structure essential for its biological activity as well as to increase the molecular weight to extend half-life for improved efficacy.

Although there have been various approaches to overcoming such challenges faced by native TRAIL (de Miguel et al. 2016), such attempts have ultimately fallen short as feasible human therapies. A leucine zipper fused TRAIL and a cross-linked TRAIL stabilized by inserted mutations creating an additional artificial disulfide bond are both potentially immunogenic in humans due to the non-human nature of their added oligomerization domains; moreover, both have demonstrated hepatotoxicity not observed with native TRAIL. Other methods for extending half-life of TRAIL have also encountered obstacles; albumin conjugated TRAIL nanoparticles must be prepared in organic solvents and production was extremely limited. Similar production issues are faced by liposome conjugated TRAIL. Recently, immuno-oncology as a paradigm for cancer therapy has made great progress with the approvals of therapeutic antibodies against PD-1, PD-L1 and CTLA-4, with exciting sustained remissions for certain cancer patients, including melanoma. Programmed cell death protein 1, also known as PD-1, is a cell surface receptor that belongs to the immunoglobulin superfamily and is expressed on T cells and pro-B cells. PD-1 binds two ligands, PD-L1 and PD-L2. PD-1 is a member of the extended CD28/CTLA-4 family of T cell regulators. PD-1 and its ligands play an important role in downregulating the immune system by preventing the activation of T-cells, which in turn reduces autoimmunity and promotes self-tolerance. The inhibitory effect of PD-1 is accomplished through a dual mechanism of promoting apoptosis (programmed cell death) in antigen-specific T cells in lymph nodes while simultaneously reducing apoptosis in regulatory T cells (suppressor T cells). Therapeutic antibodies that block PD-1 or its ligand (PD-L1) as well as CTLA-4, activate the immune system to attack tumors and are therefore used to treat cancer. These breakthroughs demonstrated that cancer is an immune disease with cancer cells evading the body's immune surveillance by inhibiting several key immune check-points such as PD-1 and CTLA-4 signaling pathways. Importantly, there is an increasing body of evidence showing that several members of TNF family of cytokines, such as 4-1BBL (also called CD137L) and OX40L, can potently stimulate proliferation and survival of antigen-specific cytotoxic T cells as well as stimulate the memory T cell response. Thus, combinational use of PD-1 or CTLA-4 antagonists with 4-1BB or OX40 agonists may fully activate the body's immune attack against cancer. Like all members of TNF family of cytokines, 4-1BBL and OX40L are small in molecular weight and homo-trimeric in structure without inter-subunit disulfide bond linkages.

Clearly, there is a great need to be able to create secreted homo-trimeric and disulfide bond-strengthened TNF family of cytokines that retain full biological activities. Compared to their native counterparts produced from bacteria, such rationally designed TNF family of ligand-Trimers produced in mammalian cells such as CHO cells, may significantly increase the efficacy for cancer treatment. To be therapeutically feasible, a desired trimerizing protein moiety for biologic drug designs should satisfy the following criteria. Ideally it should be part of a naturally secreted protein, like immunoglobulin Fc, that is also abundant (non-toxic) in the circulation, human in origin (lack of immunogenicity), relatively stable (long half-life) and capable of efficient self-trimerization which is strengthened by inter-chain covalent disulfide bonds, so the trimerized TNF family of cytokines are structurally stable.

Collagen is a family of fibrous proteins that are the major components of the extracellular matrix. It is the most abundant protein in mammals, constituting nearly 25% of the total protein in the body. Collagen plays a major structural role in the formation of bone, tendon, skin, cornea, cartilage, blood vessels, and teeth. The fibrillar types of collagen I, II, III, IV, V, and XI are all synthesized as larger trimeric precursors, called procollagens, in which the central uninterrupted triple-helical domain consisting of hundreds of “G-X-Y” repeats (or glycine repeats) is flanked by non-collagenous domains (NC), the N-propeptide and the C-propeptide. Both the C- and N-terminal extensions are processed proteolytically upon secretion of the procollagen, an event that triggers the assembly of the mature protein into collagen fibrils which forms an insoluble cell matrix. BMP-1 is a protease that recognizes a specific peptide sequence of procollagen near the junction between the glycine repeats and the C-prodomain of collagens and is responsible for the removal of the propeptide. The shed trimeric C-propeptide of type I collagen is found in human sera of normal adults at a concentration in the range of 50-300 ng/mL, with children having a much higher level which is indicative of active bone formation. In people with familial high serum concentration of C-propeptide of type I collagen, the level could reach as high as 1-6 μg/mL with no apparent abnormality, suggesting the C-propeptide is not toxic. Structural study of the trimeric C-propeptide of collagen suggested that it is a tri-lobed structure with all three subunits coming together in a junction region near their N-termini to connect to the rest of the procollagen molecule. Such geometry in projecting proteins to be fused in one direction is similar to that of Fc dimer.

Type I, IV, V and XI collagens are mainly assembled into heterotrimeric forms consisting of either two α-1 chains and one α-2 chain (for Type I, IV, V), or three different a chains (for Type XI), which are highly homologous in sequence. The type II and III collagens are both homotrimers of α-1 chain. For type I collagen, the most abundant form of collagen, stable α(I) homotrimer is also formed and is present at variable levels in different tissues. Most of these collagen C-propeptide chains can self-assemble into homotrimers, when over-expressed alone in a cell. Although the N-propeptide domains are synthesized first, molecular assembly into trimeric collagen begins with the in-register association of the C-propeptides. It is believed the C-propeptide complex is stabilized by the formation of interchain disulfide bonds, but the necessity of disulfide bond formation for proper chain registration is not clear. The triple helix of the glycine repeats and is then propagated from the associated C-termini to the N-termini in a zipper-like manner. This knowledge has led to the creation of non-natural types of collagen matrix by swapping the C-propeptides of different collagen chains using recombinant DNA technology. Non-collagenous proteins, such as cytokines and growth factors, also have been fused to the N-termini of either pro-collagens or mature collagens to allow new collagen matrix formation, which is intended to allow slow release of the noncollagenous proteins from the cell matrix. However, under both circumstances, the C-propeptides are required to be cleaved before recombinant collagen fibril assembly into an insoluble cell matrix.

Although, other protein trimerization domains, such as those from GCN4 from yeast fibritin from bacteria phage T4 and aspartate transcarbamoylase of Escherichia coli, have been described previously to allow trimerization of heterologous proteins, none of these trimerizing proteins are human in nature, nor are they naturally secreted proteins. As such, any trimeric fusion proteins would have to be made intracellularly, which not only may fold incorrectly for naturally secreted proteins such as soluble receptors, but also make purification of such fusion proteins from thousands of other intracellular proteins difficult. Moreover, the fatal drawback of using such non-human protein trimerization domains (e.g. from yeast, bacteria phage and bacteria) for trimeric biologic drug design is their presumed immunogenicity in the human body, rendering such fusion proteins ineffective shortly after injecting them into the human body.

One secreted protein previously used as a protein trimerization tag is tetranectin, which is a plasminogen-binding protein of C-lectin family. However, unlike IgG Fc dimerization tag, the trimeric tetranectin structure is not strengthened by any interchain disulfide bonds, and significant fractions of both monomeric and dimeric tetranectin co-existed with the trimeric structure in solution. Physiologically, teranectin is involved in tissue remodeling and increased cell matrix concentration of tetranectin in human has been linked to multiple cancer types. Recombinant heterologous tetranectin fusion proteins have only been produced intracellularly in E. coli as insoluble inclusion bodies that required refolding to obtain soluble structures. These unfavorable attributes suggest that tetranectin is not ideal for therapeutic applications as a protein trimerization tag. Nonetheless, bacterially produced ApoAl-Tetranectin fusion protein has been produced and patented and is being tested as a therapeutic agent for atherosclerosis.

SUMMARY OF THE INVENTION

There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting.

Disclosed here is an invention that allows any TNF family of cytokines (ligands) to be made into disulfide bond-linked trimeric forms as secreted proteins. The essence of the invention is to fuse a signal peptide in-frame to any the N-terminus of a soluble TNF family of cytokines, which in turn is fused in-frame to the C-propeptide domain of a collagen, which is capable of self-trimerization, using recombinant DNA technology or via total gene synthesis. The resulting DNA construct encoding such fusion proteins when expressed in eukaryotic cells are secreted as soluble proteins essentially 100% in trimeric forms covalently strengthened by inter-molecular disulfide bonds formed among three C-propeptides. The resulting trimeric TNF family of cytokines are fully active and can be purified for therapeutic applications.

In one aspect of the invention, a secreted fusion protein comprises a soluble ligand from TNF family of cytokines joined by in-frame fusion to a C-terminal portion of collagen which is capable of self-trimerization to form a disulfide bond-linked trimeric fusion protein. In another aspect of the invention, a secreted fusion protein disclosed above, wherein the soluble ligand from TNF family of cytokines is selected from the group consisting of TRAIL, TNF

, 41BBL, OX40L, GITRL, HVEML, CD27L, CD30L, RANKL, BLyS, CD40L, DR3L and APRIL.

In one aspect of the invention, a secreted TNF family of trimeric fusion protein wherein the C-terminal portion of collagen is selected from the group consisting of pro.alpha.1(I), pro.alpha 2(I), pro.alpha.1(II), pro.alpha.1(III), pro.alpha.1(V), pro.alpha.2(V), pro.alpha.1(XI), pro.alpha.2(XI) and pro.alpha.3(XI). In one aspect of the invention, a secreted TNF family of trimeric fusion protein wherein the C-terminal portion of collagen further comprises a C-propeptide without any glycine-repeat triple helical regions of collagen. In one aspect of the invention, a secreted TNF family of trimeric fusion protein wherein the C-terminal portion of collagen further comprises a glycine-repeat triple helical region of collagen linked to a C-propeptide. In one aspect of the invention, a secreted TNF family of trimeric fusion protein wherein the C-terminal portion of collagen further comprises a mutated or deleted BMP-1 protease recognition sequence.

In a preferred embodiment, the secreted fusion protein, wherein the soluble ligand from TNF family of cytokines is TRAIL, and the C-terminal portion of collagen of pro.alpha.1(I) comprises a mutated BMP-1 protease recognition sequence comprising the amino acid sequences set forth in either SEQ ID NO 1 or SEQ ID NO 2.

In another preferred embodiment, the secreted fusion protein, wherein the soluble ligand from TNF family of cytokines is 4-1BBL, and the C-terminal portion of collagen comprises pro.alpha.1(I) with a mutated BMP-1 protease recognition sequence comprising the amino acid sequences set forth in either SEQ ID NO 3 or SEQ ID NO 4.

In yet another preferred embodiment, the secreted fusion protein, wherein the soluble ligand from TNF family of cytokines is OX40L, and the C-terminal portion of collagen comprises pro.alpha.1(I) with a deleted BMP-1 protease recognition sequence comprising the amino acid sequences set forth in either SEQ ID NO 5 or SEQ ID NO 6.

In one embodiment, the secreted fusion protein, wherein the soluble ligand from TNF family of cytokines is TNF

, and the C-terminal portion of collagen comprises pro.alpha.1(I) with a mutated BMP-1 protease recognition sequence comprising the amino acid sequence set forth in SEQ ID NO 7.

In one aspect of the invention, a method for treating cancer in a mammal comprises administering to said mammal a therapeutically effective amount of a disulfide bond-linked trimeric TRAIL fusion protein comprising the amino acid sequences set forth in either SEQ ID NO 1 or SEQ ID NO 2.

In a preferred embodiment, a method for treating cancer in a mammal, wherein the cancer is gastrointestinal cancer including those from colorectal, gastric, esophageal and pancreatic origins, comprises administering to said mammal a therapeutically effective amount of a disulfide bond-linked trimeric TRAIL fusion protein. In another preferred embodiment, a method for treating cancer in a mammal, wherein the cancer is malignant ascites, comprises administering to said mammal a therapeutically effective amount of a disulfide bond-linked trimeric TRAIL fusion protein. In varying embodiments, the various compositions taught in the present invention may be used to treat any type of cancer. Additional examples of cancers that may be treated include, but are not limited to: lung cancer, pancreatic cancer, ovarian cancer, malignant ascites, and peritoneal carcinomatosis.

In one aspect of the invention, a method for treating cancer in a mammal comprises administering to said mammal a therapeutically effective amount of anti-PD1, anti-PD-L1 or anti-CTLA-4 plus a disulfide bond-linked trimeric 4-1BBL fusion protein with amino acid sequences set forth in either SEQ ID NO 3 or SEQ ID NO 4.

In yet another aspect of the invention, a method for treating cancer in a mammal comprises administering to said mammal a therapeutically effective amount of anti-PD1, anti-PD-L1 or anti-CTLA-4 plus a disulfide bond-linked trimeric OX40L fusion protein with an amino acid sequences set forth in either SEQ ID NO 5 or SEQ ID NO 6.

In one aspect of the invention, a method for treating cancer in a mammal comprises administering to said mammal a therapeutically effective amount the disulfide bond-linked trimeric fusion protein via either intravenous injection, intraperitoneal infusion or subcutaneous injection.

In another aspect of the invention, a method for treating cancer in a mammal comprises administering to said mammal a therapeutically effective amount of the disulfide bond-linked trimeric fusion protein in a series of doses separated by intervals of days or weeks.

In one aspect of the invention, a method for treating cancer in a mammal comprises administering to said mammal a therapeutically effective amount of the disulfide bond-linked trimeric fusion protein in combination with chemotherapy or inhibitors that blocks Ras signaling pathways.

In a preferred embodiment, a method for treating cancer in a mammal comprises administering to said mammal a therapeutically effective amount of TRAIL-Trimer in combination with Sulindac which inhibits NF

B pathway which is downstream of Ras.

In another preferred embodiment, a method for treating cancer in a mammal comprises administering to said mammal a therapeutically effective amount of TRAIL-Trimer in combination with an EGFR inhibitor, such as Iressa.

In another aspect of the invention, a method for treating malignant ascites in a mammal comprises administering to said mammal via intraperitoneal injection/infusion a therapeutically effective amount of TRAIL-Trimer or TRAIL.

The following are the advantages of this invention: (1) collagen is the most abundant protein secreted in the body of a mammal, constituting nearly 25% of the total proteins in the body; (2) the major forms of collagen naturally occur as trimeric helixes, with their globular C-propeptides being responsible for the initiating of trimerization; (3) the trimeric C-propeptide of collagen proteolytically released from the mature collagen is found naturally at sub microgram/mL level in the blood of mammals and is not known to be toxic to the body; (4) the linear triple helical region of collagen can be included as a linker with predicted 2.9 Å spacing per residue, or excluded as part of the fusion protein so the distance between a protein to be trimerized and the C-propeptide of collagen can be precisely adjusted to achieve an optimal biological activity; (5) the recognition site of BMP1 which cleaves the C-propeptide off the pro-collagen can be mutated or deleted to prevent the disruption of a trimeric fusion protein; (6) the C-propeptide domain self-trimerizes via disulfide bonds and it provides a universal affinity tag, which can be used for purification of any secreted fusion proteins created by this invention.

In contrast to any TNF family of cytokines such as TRAIL, TRAIL-Trimer (designated SCB-313) is covalently linked homo-trimer, thus theoretically more stable than the native and non-covalently bonded trimers such as TRAIL (FIG. 1).

In contrast to the Fc Tag technology, with which secreted dimeric fusion proteins can be created, this timely invention disclosed herein enables the creation and secretion of soluble, disulfide bond-linked trimeric fusion proteins from TNF family of cytokines at high level (FIG. 2 and FIG. 3). Given the fact that a homotrimer has 3-fold symmetry, whereas a homodimer has only 2-fold symmetry, the two distinct structural forms theoretically can never be perfectly overlaid (FIG. 1). Consistently, we demonstrated that TRAIL-Trimer created by this invention with its amino acid sequence composition set forth in SEQ ID NO 2 is over 100 times more potent in cancer cell killing (IC50=67 ng/mL) compared to TRAIL-Fc dimer (IC50=6700 ng/mL) (FIG. 1 and FIG. 7).

In addition to structural stability, the trimerized TNF family of fusion cytokines have significantly increased molecular weight (>160 Kda) than their corresponding native cytokines (˜60 Kda), thus are predicted and confirmed to have longer half lives in sera due to less leakage through renal filtration when administered into the body (FIG. 8). The high potency of disulfide bond-linked trimeric TNF family of cytokines with extended sera half lives increased the drug exposure to the tumor cells and led to significant improvement in tumor reduction in vivo, compared to native TRAIL (FIG. 9).

Finally we also discovered that, in contrast to the rapid systemic elimination of native TNF family of cytokines leading to their very short half-lives, both native TRAIL and TRAIL-Trimer showed dramatically longer half-lives in tumor ascites in the intraperitoneal cavity of mice, with T_(1/2) measured in hours instead of minutes compared to that in sera. Since treatment of malignant ascites is still an unmet medical need for many end-stage cancer patients, particularly from gastrointestinal and gynecological cancer origins, TRAIL-Trimer as well as native TRAIL may be used to treat metastatic ascites, given their tumor cell killing efficacy in vivo clearly hinges on their stability and sustained exposure to tumors. To this end we demonstrated that subcutaneous-inoculation of human gastric cancer cell line (SNU-16) isolated from a patient's malignant ascites is very sensitive to TRAIL-Trimer (FIG. 14), and this finding would predict that TRAIL-Trimer and TRAIL may also be used to more effectively treat human malignant ascites caused by tumor cells that have metastasized to the intraperitoneal cavity.

There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto.

These together with other objects of the invention, along with the various features of novelty, which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will be apparent from the following detailed description of embodiments thereof, which description should be considered in conjunction with the accompanying drawings, in which:

FIG. 1 is schematic representation of structure differences of TRAIL polypeptides used in this study. Upper panel: Three recombinant soluble forms of human TRAIL have been used in this study: a native TRAIL comprised of the extracellular domain of TRAIL, a dimeric TRAIL-Fc comprised of extracellular TRAIL domain fused to human IgG1 Fc domain, and a TRAIL-Trimer comprised of extracellular TRAIL domain fused to the C-prodomain of a Type I collagen (Trimer-Tag) with a mutated BMP-1 site. Amino acid sequence lengths are shown for each protein and domain respectively. Lower panel: Theoretical molecular weights (kDa) of both monomeric and multimeric forms of native TRAIL, TRAIL-Fc and TRAIL-Trimer, respectively. Native TRAIL associates into a noncovalently-linked homotrimer, TRAIL-Fc forms a covalently-linked homodimer, and TRAIL-Trimer forms a covalently-linked homotrimer.

FIG. 2 is SDS-PAGE analysis by Coomasie blue staining of high level expression of TRAIL-Trimer (SEQ ID NO 1) in GH-CHO cells (GenHunter Corporation) in a serum free fed-batch bioprocess over 13 days in a 10 L bioreactor (NBS). Cells were seed at 0.3 million/mL and cultured in SFM4CHO medium (Hyclone) and 10% Cell Boost 2 (Hyclone) was fed every other day from Day 4. 10 microliter of cell culture media from each day were analyzed under either non-reducing or reducing condition to demonstrate that TRAIL-Trimer was covalently (disulfide bonds) linked homo-trimer as indicated. The molecular weight marker (Tru Blue, from BioRad) was used as control. The estimated final titer of TRAIL-Trimer expression was around 0.4 mg/mL.

FIG. 3 is bioassay analysis of TRAIL-Trimer production in conditioned medium from Day 5 to Day 13 from the fed-batch cell culture of CHO cells overexpressing TRAIL-Trimer.

FIG. 4 is SDS-PAGE and Western blot analysis of purified TRAIL-Trimer under either non-reducing or reducing conditions. TRAIL-Trimer was sequentially purified from the cell culture medium with hydrophobic interaction chromatography (HIC) followed by ultrafiltration (UF) to change buffer and then via an anion-exchange chromatography (Q) with a 0.2M NaCl elution in 10 mM Tris-Cl, pH 8.2 buffer. After a final polishing with Seperdex 200 gel filtration chromatography (GE health Sciences), the final purified TRAIL-Trimer was more than 90% pure with an IC50 about 100 ng/mL (1 U). Two μg of purified protein was analyzed by a 10% SDS-PAGE and stained with Coomassie Blue. Zero point two μg of purified protein was analyzed by Western blot using monoclonal antibody against TRAIL-domain and Trimer-domain, respectively.

FIG. 5 is purity evaluation of TRAIL-Trimer and TRAIL-Fc. SDS-PAGE analysis of purified TRAIL-Trimer and TRAIL-Fc under either non-reducing or reducing conditions. 2 μg of purified protein was analyzed by 10% or 15% SDS-PAGE, respectively, and stained with Coomassie Blue.

FIG. 6 is the comparison of bioactivity for TRAIL-Trimer, TRAIL-Fc and native TRAIL. The IC₅₀ value of TRAIL-Trimer, TRAIL-Fc and native TRAIL were assessed using a TRAIL sensitive cell line COLO205 on a Real-Time Cell Analysis (RTCA) system. The IC₅₀ value was obtained according to the dose-response cell index (CI) curve. The IC50 value of TRAIL-Trimer, TRAIL-Fc and native TRAIL is 23.2 ng/mL, 260.8 μg/mL, and 6.7 ng/mL, respectively, before IC₅₀ values were molar ratio-adjusted based on theoretical molecular weights for each protein.

FIG. 7 is the kinetic studies of TRAIL-Trimer, TRAIL-Fc and native TRAIL binding to the soluble DR5-Fc fusion protein assessed by biolayer interferometry measurements. The Super Streptavidin biosensor tips of the ForteBio Octet RED 96 were coated with biotinylated DR5-Fc. The biosensor tips were dipped in increasing concentrations gradient of TRAIL-Trimer, TRAIL-Fc and native TRAIL to measure their binding to DR5-Fc and subsequently moved to wells containing buffer (PBS) to measure dissociation rates. The dissociation constant Kd was shown for each graph.

FIG. 8 is pharmacokinetic profile of TRAIL-Trimer determined by TRAIL bioassay with colo205 cells. Mice and rats were injected intravenously with TRAIL-Trimer at 80 mg/kg (n=5 for each species). Relative serum concentrations of TRAIL-Trimer were evaluated at periodic intervals by TRAIL bioassay with colo205 cells.

FIG. 9 is the in vivo antitumor activities of TRAIL-Trimer and native TRAIL. (Upper panel) Nude mice with established COL0205 xenografts were given TRAIL-Trimer (30, 50, or 80 mg/kg/day) or vehicle as an i.v. bolus for 5 consecutive days (n=6/group). Results shown are group mean (±S.D.). (Lower panel) Nude mice with established COL0205 xenografts were given the same molar concentration of TRAIL-Trimer (80 mg/kg/day) and native TRAIL (30 mg/kg/day). Results shown are group mean (±S.D.).

FIG. 10 is SDS-PAGE analysis by Coomasie blue staining of high level expression of human 4-1BBL-Trimer (SEQ ID NO. 4) in GH-CHO cells (GenHunter Corporation) in a serum free fed-batch bioprocess over 7 days in a 10 L bioreactor. Cells were seed at 0.3 million/mL and cultured in SFM4CHO medium (Hyclone) and 10% Cell Boost 2 (Hyclone) was fed every other day from Day 4. 10 microliter of cell culture media from each day were analyzed under either non-reducing (Left Panel) or reducing condition (right panel) to demonstrate that 4-1BBL-Trimer was covalently (disulfide bonds) linked homo-trimer as indicated by arrow heads. The molecular weight marker (Tru Blue, from BioRad) was used as control.

FIG. 11 is SDS-PAGE analysis of purified 4-1BBL-Trimer under non-reducing condition. 4-1BBL-Trimer was expressed in CHO cells under serum-free condition and sequentially purified from the cell culture medium (M) with Blue Sepharose chromatography (Blue) followed by ultrafiltration (UF) to change buffer and concentration, and then via Superdex 200 gel filtration chromatography. The molecular weight size markers (MW) were as in FIG. 2.

FIG. 12 is SDS-PAGE analysis of purified 4-1BBL and 4-1BBL-Trimer under either non-reducing or reducing conditions. Note the purified native-like 4-1BBL expressed in E. coli, unlike 4-1BBL-Trimer is a disulfide bond linked trimer. The molecular weight size markers (MW) were as in FIG. 2.

FIG. 13 is functional characterization of purified 4-1BBL vs. 4-1BBL-Trimer in stimulation of PBMC production of IL-8. Both 4-1BBL vs. 4-1BBL-Trimer had similar IC50 in stimulating PBMC in IL-8 production, with IC50 being 0.5-0.6 pmole/mL.

FIG. 14 is pharmacokinetic profile TRAIL-Trimer in ascites. Balb/c mice with ascites developed via inoculation of a hybridoma cell line unrelated to TRAIL were injected intraperitoneally with either 10 mg/kg (upper panel) or 80 mg/kg (lower panel) of TRAIL-Trimer (n=2 for each dosing). Relative concentration of TRAIL-Trimer was evaluated at periodic intervals using the standard bioassay (colo205 cells) and fluid taken from the ascites. The estimated half-life of TRAIL-Trimer was in the range of 4-5 hrs.

FIG. 15 is pharmacokinetic profile of native TRAIL (nTRAIL) in mouse ascites. Balb/c mice with ascites developed via inoculation of a hybridoma cell line unrelated to TRAIL were injected intraperitoneally with 10 mg/kg (n=2). Relative concentration of TRAIL-Trimer was evaluated at periodic intervals with fluid taken from the ascites using the standard bioassay (colo205 cells) and Western blot analysis. The estimated half-life of TRAIL was in the range of 2-5 hrs.

FIG. 16. is the in vivo antitumor activities of TRAIL-Trimer against SNU-16 which is a human gastric cancer cell line established from metastatic ascites. Nude mice with established subcutaneous xenografts of SNU-16 cells were given TRAIL-Trimer (20, 40, or 80 mg/kg/day) or vehicle as an i.v. bolus for 5 consecutive days (n=6/group). As a control, we also delivered TRAIL-Trimer at 80 mg/kg/day) for 5 consecutive days via intraperitoneal (i.p.) injections (n=6/group).

DESCRIPTION OF SEQUENCE LISTINGS

SEQ ID NO 1 (479 amino acids): Shows the amino acid sequence for TRAIL-Trimer with native soluble human TRAIL sequence.

SEQ ID NO 2 (482 amino acids): Shows the amino acid sequence for TRAIL-Trimer (variant 1) with a modified N-terminus of soluble human TRAIL sequence.

SEQ ID NO 3 (495 amino acids): Shows the amino acid sequence for 4-1BBL-Trimer with native soluble human T4-1BBL sequence.

SEQ ID NO 4 (498 amino acids): Shows the amino acid sequence for 4-1BBL-Trimer (variant 1) with a modified N-terminus of soluble human TRAIL sequence.

SEQ ID NO 5 (444 amino acids): Shows the amino acid sequence for OX40L-Trimer with native soluble human OX40L sequence.

SEQ ID NO 6 (447 amino acids): Shows the amino acid sequence for OX40L-Trimer (variant 1) with a modified N-terminus of soluble human OX40L sequence.

SEQ ID NO 7 (403 amino acids): Shows the amino acid sequence for TNF

-Trimer with native soluble human OX40L sequence.

DETAILED DESCRIPTION OF THE EMBODIMENTS

While several variations of the present invention have been illustrated by way of example in particular embodiments, it is apparent that further embodiments could be developed within the spirit and scope of the present invention, or the inventive concept thereof. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention, and are inclusive, but not limited to the following appended claims as set forth.

Prior to setting forth the invention, it may be helpful to an understanding thereof to set forth definitions of certain terms to be used hereinafter.

DNA Construct: A DNA molecule, generally in the form of a plasmid or viral vector, either single- or double-stranded that has been modified through recombinant DNA technology to contain segments of DNA joined in a manner that as a whole would not otherwise exist in nature. DNA constructs contain the information necessary to direct the expression and/or secretion of the encoding protein of interest.

Signal Peptide Sequence: A stretch of amino acid sequence that acts to direct the secretion of a mature polypeptide or protein from a cell. Signal peptides are characterized by a core of hydrophobic amino acids and are typically found at the amino termini of newly synthesized proteins to be secreted or anchored on the cell surface. The signal peptide is often cleaved from the mature protein during secretion. Such signal peptides contain processing sites that allow cleavage of the signal peptides from the mature proteins as it passes through the protein secretory pathway. A signal peptide sequence when linked to the amino terminus of another protein without a signal peptide can direct the secretion of the fused protein. Most of the secreted proteins, such as growth factors, peptide hormones, cytokines and membrane proteins, such as cell surface receptors, contain a signal peptide sequence when synthesized as a nascent protein.

Soluble receptor: The extracellular domain, in part or as a whole, of a cell surface receptor, which is capable of binding its ligand. Generally, it does not contain any internal stretch of hydrophobic amino acid sequence responsible for membrane anchoring.

C-propeptide of collagens: The C-terminal globular, and non-triple-helical domain of collagens, which is capable of self-assembly into trimers. In contrast to the triple helical region of collagens, the C-propeptide does not contain any glycine repeat sequence and is normally proteolytically removed from procollagen precursor upon procollagen secretion before collagen fibril formation.

Glycine repeats: The central linear triple helix forming region of collagen which contains hundreds of (Gly-X-Y)_(n) repeats in amino acid sequence. These repeats are also rich in proline at X or/and Y positions. Upon the removal of N- and C-propeptides, the glycine-repeats containing collagen triple helices can assemble into higher order of insoluble collagen fibrils, which make up the main component of the cell matrix. cDNA: Stands for complementary DNA or DNA sequence complementary to messenger RNA. In general cDNA sequences do not contain any intron (non-protein coding) sequences.

One of the modern strategies for treating autoimmune diseases involves the use of biologic TNF antagonists, such as soluble receptors or therapeutic antibodies.

However, current TNF-α biologic blockers are all dimeric in structure, whereas TNF-α itself is homotrimeric in nature. Here we describe a general methodology for efficient creation of trimeric soluble receptors. The process involves gene fusion between a soluble receptor with a ligand binding domain and a trimerization tag from the C-propeptide domain of pro-collagen (TRIMER tag), which is capable of self-assembly into a covalently linked trimer. Using both in vitro bioassays and an in vivo mouse model for collagen-induced arthritis (CIA), we show that the homotrimeric soluble TNF receptor produced with such method is a more potent blocker than dimeric TNF receptor decoys in inhibiting TNF-α signaling. Thus, TRIMER tag provides a new platform for rational design of the next generation biologic drugs against autoimmune diseases.

Prior to this invention, nearly all therapeutic antibodies and soluble receptor-Fc fusion proteins, such as Enbrel®, are dimeric in structure. Although these molecules, compared to their monomeric counterparts, have been shown to bind their target antigens or ligands with increased avidity, it is predicted that they are still imperfect, due to structural constraints, to bind their targets that have a homotrimeric structure. Examples of such therapeutically important trimeric ligands include TNF family of cytokines. Therefore, from a structural point of view, it will be desirable to be also able to generate trimeric soluble receptors or antibodies, which can perfectly dock to their target trimeric ligands, and thereby completely block the ligand actions.

This invention discloses ways for generating such secreted trimeric receptors and biological active proteins by fusing them to the C-propeptides of collagen, which are capable of self-assembly into trimers. The following are the advantages of this invention: (1) collagen is the most abundant protein secreted in the body of a mammal, constituting nearly 25% of the total protein in the body; (2) the major forms of collagen naturally occur as trimeric helixes, with their globular C-propeptides responsible for the initiating of trimerization, which are subsequently proteolytically cleaved upon triple helix formation; (3) the cleaved soluble trimeric C-propeptide of collagen is found naturally at sub microgram/mL level in the blood of mammals; (4) the linear triple helical region of collagen can be included as a linker or excluded as part of the fusion protein so the distance between a protein to be trimerized and the C-propeptide of collagen can be precisely adjusted to achieve an optimal biological activity; (5) the recognition site of BMP1 which cleaves the C-propeptide off the pro-collagen can be mutated or deleted to prevent the disruption of a trimeric fusion protein; (6) the C-propeptides domain provides a universal affinity tag, which can be used for purification of any secreted fusion proteins created by this invention; (7) unlike the IgG1 Fc tag which is known to be have other biological functions such as binding to its own cell surface receptors, the only known biological function of the C-propeptide of collagen is its ability to initiate trimerization of nascent pro-collagen chains and keep the newly made pro-collagen trimer soluble before assembly into insoluble cell matrix. These unique properties of the C-propeptide of collagen would predict that this unique trimerization tag is unlikely going to be toxic, or immunogenic, making it an ideal candidate for therapeutic applications.

Example 1: Expression, Purification and Functional Characterization of TRAIL-Trimer

Thus, trimerization via covalent bond-linkage may stabilize TRAIL/Apo2L trimeric structure essential for its biological activity as well as increase the molecular weight in order to extend half-life for improved antitumor efficacy in vivo. In this study, we show that in-frame fusion of human C-propeptide of α1(I) collagen (dubbed Trimer-Tag) to the C-terminus of mature human TRAIL leads to a disulfide bond-linked homotrimer (FIG. 1). TRAIL-Trimer (designated SCB-313) was encoded by cDNA a sequence with the following coding sequences fused in tandem: Promoter-Signal peptide-Mature TRAIL-“Trimer-Tag”. The cDNA sequence encoding the mature human TRAIL (aa 114-281 of full length human TRAIL protein) was either PCR amplified or gene synthesized and cloned into the pTrimer-T0(M) vector between HindIII and BglII sites to allow in-frame fusion with the C-prodomain of human type I (

) collagen with a mutated BMP-1 site and some glycine-rich region upstream. A short cDNA sequence encoding human TNFRII signal peptide was subsequently cloned into the HindIII site in front of the mature TRAIL to direct the secretion of the pro-TRAIL-Trimer secretion. The entire vector designated as pGH-313D was transefected into GH-CHO (dhfr−/−) cells and selected for high titer producers by step-wise gene amplification under MTX selections. The secreted mature TRAIL-Trimer with signal peptide cleaved has an amino acid sequence specified as either SEQ ID NO 1 or SEQ ID NO 2 and a 3D structure of a disulfide bond-linked Trimer denoted in FIG. 1. In contrast, the native TRAIL, which is a non-covalent linked homo-trimer, is structurally less stable as depicted in FIG. 1. As a control the same strategy was employed to create a TRAIL-Fc fusion expression construct using phFc vector (GenHunter) to allow secretion of mature TRAIL-Fc dimeric fusion protein (FIG. 1).

To produce highly pure and sufficient amounts of TRAIL-Trimer fusion protein for functional analyses, we began by screening for high-titer production clones of TRAIL-Trimer vector-transfected CHO cells via MTX-mediated gene amplification; the resulting leading clone was then adapted to serum free media and grown under fed-batch cell culture process in a bioreactor, which led to high-level expression of TRAIL-Trimer (FIG. 2). During the course of the cell culture process, samples were taken to assess the bioactivity of TRAIL-Trimer using a TRAIL-sensitive human colon cancer derived cell line—COLO205—by MTT staining (FIG. 3); as expected, bioactivity increased over time as the production of TRAIL-Trimer continued.

To obtain the TRAIL-Trimer in a highly pure form, TRAIL-Trimer from serum-free conditioned medium was purified to homogeneity by consecutive chromatographic separation steps using Blue Sepharose, Capto Q column and gel filtration. The purified TRAIL-Trimer fusion protein was characterized by SDS-PAGE under either non-reducing or reducing conditions followed by Coomassie blue staining (FIG. 4, left panel). The results clearly indicated that TRAIL-Trimer formed a disulfide bond-linked trimer as predicted. Western blot analysis using either a polyclonal antibody detecting human native TRAIL or a monoclonal antibody specific to the Trimer-Tag domain confirmed the structural feature and integrity of the fusion protein (FIG. 4, middle and right panels), which existed essentially as a covalently-linked homotrimer under non-reducing conditions. It was evident that the monoclonal antibody to the Trimer-Tag domain could only recognize the epitope under the non-reducing condition, consistent with the structure of the antigen used for the immunization to generate the antibody.

Structural Comparison of TRAIL-Trimer, TRAIL-Fc and Native TRAIL

To systematically compare TRAIL-Trimer with either a dimeric TRAIL (dulanermin) or a native TRAIL, we also produced a recombinant TRAIL-Fc fusion protein from CHO cells and native TRAIL from E. coli, following the strategy of dulanermin production (FIG. 1). After purification, all three proteins were analyzed first by SDS-PAGE under both non-reducing and reducing conditions to verify their respective structures. The results confirmed that TRAIL-Trimer maintained a homotrimer structure, whereas TRAIL-Fc was a disulfide bond-linked dimer, and native TRAIL was noncovalently-linked trimer (FIG. 5), consistent with previous studies indicating that the homotrimer of native TRAIL is maintained via hydrophobic interfaces on adjacent subunits that are weak and noncovalent in nature.

Comparison of TRAIL-Trimer, TRAIL-Fc and Native TRAIL Bioactivity In Vitro

The bioactivity IC₅₀ values of TRAIL-Trimer, TRAIL-Fc and native TRAIL were assessed using a TRAIL-sensitive human colon cancer cell line—COLO205—via Real-Time Cell Analysis (RTCA) system. Dose-response curves were generated based on cell viability, and the IC₅₀ values were obtained according to the dose-response cell index (CI) curve. COLO205 cells were exposed to increasing concentrations of TRAIL-Trimer, TRAIL-Fc or native TRAIL for 16 hr, and IC₅₀ values for TRAIL-Trimer, TRAIL-Fc and native TRAIL were determined to be 23.2 ng/ml, 260.8 μg/mL and 6.7 ng/mL, respectively. Because the predicted molecular weights of TRAIL-Trimer (˜162 kDa) and TRAIL-Fc (˜96 kDa) are both significantly larger than native TRAIL (˜60 kDa) due to their fused Trimer-Tag and Fc domains respectively (FIG. 1), we then calculated the molar ratio-adjusted IC₅₀ values in order to more accurately compare the bioactivities of TRAIL-domains present in each protein. On a molar ratio-adjusted basis, the IC₅₀ values for TRAIL-Trimer, TRAIL-Fc and native TRAIL were 0.12 nM, 2716.7 nM and 0.15 nM, respectively (FIG. 6). These results demonstrate that the bioactivity of trimeric forms of TRAIL is over 4 orders of magnitude higher than that of dimeric TRAIL, which may explain why previous agonist mAbs to DR4 and DR5 failed in clinical trials. A previous concern for TRAIL-Trimer was if the natural bioactivity of the trimeric TRAIL conformation could be preserved in the fusion protein; the results presented here clearly demonstrate that the bioactivities of TRAIL-Trimer and native TRAIL are equivalent.

Comparison of TRAIL-Trimer, TRAIL-Fc and Native TRAIL in Receptor Binding Avidity In Vitro

DR5 (TRAIL-R2) is one of TRAIL's functional receptors which initiates extrinsic apoptosis pathway signaling upon activation; thus, we examined the binding kinetic profile of TRAIL-Trimer, TRAIL-Fc and native TRAIL to a soluble DR5-Fc fusion protein. With Fortebio biolayer interferometry measurement, the biotin-labeled DR5-Fc was first captured on Streptavidin (SA) sensors, and real-time binding curves were measured and plotted by applying the sensor in gradient concentrations (15.4 nM-123.5 nM) of the three analytes (FIG. 7). TRAIL-Trimer was observed to have picomolar binding affinity to DR5-Fc (K_(D)<1.0×10⁻¹²M). Unsurprisingly, the dimeric TRAIL-Fc exhibited a receptor binding affinity over 4 orders of magnitude lower (K_(D)=1.85×10⁻⁸M) than that of TRAIL-Trimer. Interestingly, the DR5-Fc binding affinity of TRAIL-Trimer was over two orders of magnitude higher than that of native TRAIL (K_(D) of 2.63×10⁻¹⁰M). While native TRAIL bound to DR5-Fc (K_(on)=1.75×10⁻⁵ s⁻¹) twice as fast as TRAIL-Trimer (K_(on)=8.1×10⁴ Ms⁻¹), native TRAIL dissociated (K_(off)=4.6×10⁻⁵ s⁻¹) from DR5-Fc ata rate >460 times faster than TRAIL-Trimer (K_(off)<1×10⁻⁷ s⁻¹). This is consistent with the trimeric conformation being the fully active form for TNF family of cytokines and explained why DR4 and DR4 receptor agonist antibodies (made by Human Genome Sciences Inc. and Amgen), which were all dimeric in structures, had low activity and failed in multiple human clinical trials against cancer. This is also why often anti-Fc antibodies are needed to enhance the potency of such agonist antibodies by cross-linking them to oligomers.

These results suggest that the covalent nature of the homotrimeric linkages in TRAIL-Trimer may stabilize the ligand-receptor binding, while the noncovalent trimerization of native TRAIL assumes a conformation more susceptible to dissociation form the receptor.

Pharmacokinetic Profile of TRAIL-Trimer Vs. Native TRAIL in Mice

We examined the pharmacokinetic profiles for TRAIL-Trimer; nude mice and Lewis rats were injected intravenously (i.v.) with TRAIL-Trimer (80 mg/kg), and relative serum concentration of the protein was evaluated at periodic intervals by TRAL bioassay using colo 205 cells. The half-life of TRAIL-Trimer was determined to be 24.5 min and 20 min for nude mice and Lewis rats, respectively (FIG. 8), representing an approximately 5-fold longer half-life than that of native TRAIL previously reported. These results indicate that TRAIL-Trimer is less rapidly eliminated and is more stable than native TRAIL in vivo.

Comparison of Antitumor Activity of TRAIL-Trimer and Native TRAIL In Vivo

We then examined the ability of TRAIL-Trimer and native TRAIL to kill human tumor cells in vivo by using a common tumor xenograft model in nude mice. After subcutaneous tumors from inoculated COLO205 human colon cancer cell line had grown to an average size of ˜270 mm³, mice were randomized (n=6/group), and TRAIL-Trimer doses of 30 mg/kg, 50 mg/kg or 80 mg/kg were given intravenously once-daily over the first 5 days of the study. Tumor sizes rapidly decreased following TRAIL-Trimer administration in a dose-dependent fashion (FIG. 9, upper panel). In contrast, tumors from mice that had been administered with formulation buffer (negative control) grew rapidly and continuously.

The dose-response of TRAIL-Trimer observed here suggests that the best antitumor activity with this regimen is achieved with 80 mg/kg/day, where the longest sustained antitumor response was observed. Thus, we then compared the efficacy of TRAIL-Trimer (80 mg/kg/day) to an equimolar dose of native TRAIL (30 mg/kg/day), given the approximately 2.7 fold difference in molecular weight between the two proteins. At every time point that tumor sizes were measured following dosing, tumors in mice treated with TRAIL-Trimer were smaller than in mice treated with native TRAIL (FIG. 9, lower panel), demonstrating that TRAIL-Trimer antitumor activity in vivo is superior to native TRAIL in this model. These results are consistent with the superior systemic exposure (pharmacokinetic profile) and receptor-binding affinity results also observed.

Example 2: Expression, Purification and Functional Characterization of 4-1BBL-Trimer

Immunotherapy is a rapidly expanding field in oncology, which mobilizes one's own immune system to combat the cancerous lesions. Although immune-checkpoint inhibitors such as anti-PD-1 and anti-PD-L1 antibodies have generated much excitement in “curing” certain type of deadly cancer, the relatively low response rates in the range of 15-30% indicate a need for further improvement. Of the many approaches currently under studying to boost anti-tumor immune responses, modulation of immune co-stimulatory receptors on lymphocytes in the tumor microenvironment has thus far proven to be the most promising. Lymphocytes require two signals for optimal activation T-cell receptor (TCR) ligation and costimulation. Costimulation provides an independent stimulus that influences the outcome of the interaction between T cells and antigen-presenting cells (APC). Without costimulation antigen primed T cells will undergo apoptosis or become anergic. 4-1BB (CD137) and OX40 are costimulatory members of the TNFR family, which are induced when T cells receive antigen-specific signals. Their ligands, 4-1BBL (CD137L) and OX40L, are also induced on antigen-presenting cells, such as dendritic cells, macrophages, and B cells. The 4-1BBL-4-1BB pathway co-stimulates T cells to carry out effector functions such as eradication of established tumors and the broadening of primary and memory CD8 T cell responses. 4-1BB-mediated signals have been shown to induce a novel subpopulation of CD11c⁺CD8⁺T cells that have strong anti-cancer and anti-autoimmune effects. Binding of the 4-1BB ligand (4-1BBL) to its receptor, 4-1BB provides the T lymphocyte with co-stimulatory signals for survival, proliferation, and differentiation. The 4-1BBL pathway is becoming a well-known target for anti-cancer immunotherapy. In contrast to immune checkpoint blocking antibodies, 4-1BB agonists can both potentiate anti-tumor and anti-viral immunity, while at the same time ameliorating autoimmune diseases.

In this invention, we also used Trimer-TAG technology developed in our laboratory to express the recombinant 4-1BBL-Trimer in CHO cells (FIG. 10), following the same strategy as described above for TRAIL-Trimer. The secreted mature 4-1BBL-Trimer with signal peptide cleaved has an amino acid sequence specified as either SEQ ID NO 3 or SEQ ID NO 4. 4-1BBL-Trimer was purified to near homogeneity using multiple chromatography approaches including Blue-Sepharose and Superdex 200 gel filtration chromatography (FIG. 11) and shown to be a disulfide bond-linked trimer in comparison to recombinant native-like 4-1BBL which is not a covalently linked trimer (FIG. 12). We show that the purified 4-1BBL-Trimer has similar biological activity as native 4-1BBL in activating PBMC, which leads to IL-8 production (FIG. 13). Thus the recombinant 4-1BBL and 4-1BBL-Trimer may be used as potential immuno-costimulators in the next generation of immune-oncology drugs.

We also determined the pharmacokinetic behavior of 4-1BBL-Trimer in Balb/c mice (n=3) and showed that the t1/2 of 4-1BBL-Trimer was 16 min, which is 4-5 times longer that that of native 4-1BBL previous reported.

Example 3: Expression, Purification and Functional Characterization of OX40L-Trimer

Since OX40L has similar biological functions as 4-1BBL, we also produced OX40L-Trimer following the same strategy. The secreted mature OX40L-Trimer with signal peptide cleaved has an amino acid sequence specified as either SEQ ID NO 5 or SEQ ID NO 6.

Example 4: Pharmacokinetic Profiles of TRAIL-Trimer and Native TRAIL in Tumor Ascites and In Vivo Anti-Tumor Activity TRAIL-Trimer Against Human Cancer Cells Derived from Metastatic Ascites of Human Gastric Cancer

Balb/c mice with ascites developed via inoculation of a hybridoma cell line were injected intraperitoneally with either 10 mg/kg (upper panel) or 80 mg/kg (lower panel) of TRAIL-Trimer (n=2 for each dosing). Relative concentration of TRAIL-Trimer was evaluated at periodic intervals using the standard bioassay (colo205 cells) and fluid taken from the ascites. Rather surprisingly, the half-life of TRAIL-Trimer was shown to be in the range of 4-5 hrs (FIG. 14). Interestingly, we showed that the native TRAIL (10 mg/kg) also was turned over much slower in tumor ascites than that in sera, with a half-life around 2-3 hrs (FIG. 15), in comparison to 3-5 min in sera via i.v. injection. Compared to their quick elimination in sera, the extremely long half-lives of both TRAIL-Trimer and native TRAIL discovered in our studies immediately suggest that treatment of metastatic ascites caused by the tumor cells metastasized to the stomach cavity may be an ideal indication for both TRAIL-Trimer and native TRAIL.

To this end, we went on to demonstrate the efficacy in vivo antitumor activities of TRAIL-Trimer against SNU-16 which is a human gastric cancer cell line established from metastatic ascites. Nude mice with established subcutaneous xenografts of SNU-16 cells were given TRAIL-Trimer (20, 40, or 80 mg/kg/day) or vehicle as an i.v. bolus for 5 consecutive days (n=6/group). As a control, we also delivered TRAIL-Trimer at 80 mg/kg/day) for 5 consecutive days via intraperitoneal injections (n=6/group). The results shown in FIG. 16 demonstrated that, like colo205 cells, human gastric cancer cells derived from metastatic ascites were very sensitive to TRAIL-Trimer via i.v. delivery of the drug. When equal dosage of TRAIL-Trimer (80 mg/kg/day) was administered via intraperitoneal injections (i.p.), the anti-tumor potency was much less compared to that via i.v. delivery of the drug. In fact the anti-tumor activity of TRAIL-Trimer at 80 mg/kg/day via i.p. injection was even less potent than i.v. delivery of the drug at 20 mg/kg/day. This finding confirms that serum absorption of TRAIL-Trimer when delivered via i.p. injection was very slow (<25%), which is consistent with the slow turnover of TRAIL-Trimer in intraperitoneal cavity or ascites fluid as described above. 

What is claimed is:
 1. A method for treating cancer in a mammal, comprising the step of administering to said mammal a therapeutically effective amount of a disulfide bond-linked trimeric TRAIL fusion proteins with an amino acid sequence composition identified by one of SEQ. ID NO. 1 or SEQ. ID NO.
 2. 2. The method of claim 1, wherein the cancer is gastronintestinal cancer.
 3. The method of claim 1, wherein the cancer is colorectal cancer.
 4. The method of claim 1, wherein the cancer is lung cancer.
 5. The method of claim 1, wherein the cancer is pancreatic cancer.
 6. The method of claim 1, wherein the cancer is ovarian cancer.
 7. The method of claim 1, wherein the cancer is a malignant ascites.
 8. The method of claim 1, wherein the cancer is peritoneal carcinomatosis.
 9. The method of claim 1, wherein the disulfide bond-linked trimeric fusion protein is administered via intravenous injection.
 10. The method of claim 1, wherein the disulfide bond-linked trimeric fusion protein is administered via intraperitoneal infusion.
 11. The method of claim 1, wherein the disulfide bond-linked trimeric fusion protein is administered via subcutaneous injection.
 12. The method of claim 1, wherein the disulfide bond-linked trimeric fusion protein is administered in a series of doses separated by intervals of days or weeks.
 13. The method of claim 1, wherein the disulfide bond-linked trimeric fusion protein is administered in combination with chemotherapy.
 14. The method of claim 1, wherein the disulfide bond-linked trimeric fusion protein is administered in combination with a Ras inhibitor. 